Process for the production of permselective membranes

ABSTRACT

Anion or cation permselective membranes or ion-exchange material is produced by sulphochlorination of a polyolefine, e.g. polyethylene, sheet 0.01-2 mm. thick in heterogeneous reaction so as to produce a water-insoluble product and replacing the chlorine atoms of the sulpho-chloride groups produced by hydroxyl or free basic radicals, e.g. by aminolysis, as required.  The sulpho-chlorination may be effected using sulphuryl chloride or sulphur dioxide and chlorine in the presence of a catalyst, e.g. strong acid or Friedel-Crafts, or under irradiation by U.V. or visible light.  The hydrolysis or aminolysis may be effected with carbon tetrachloride as swelling agent, using a di- or poly-valent amine for the aminolysis and the non-quaternary amine derivatives may be alkylated and quaternized. Both hydroxyl and free basic radicals may be introduced into the one sheet.

United States Patent Ofice Patented June 11, 1968 9 Claims. (c1. zen-2.2

This application is a continuation-in-part of our copending applicationSer. No. 154,065, filed Nov. 21, 1961, now abandoned.

The present invention relates to a process for the production ofpermseleotive membranes for use in electrodialysis.

Hydrophilic organic membranes made from hydrophobic films by introducinganionic or cationic substituents into them, are known. Substitutedchlorinated rubber and vinylic compounds in membrane form, and thepreparation of same, are also known. An improvement of this relating tothe preparation of membranes prepared from polyalkylenic base material,subjected to swelling in a monomeric aromatic vinylic compound intowhich membranes ionic groups are later introduced, is also known.

According to the present invention, there is provided a process for theproduction of permselective membranes for use in electrodialysis whichcomprises sulfochlonnating a polyolefine sheet in heterogenous reactionso as to result in a substantially water-insoluble product, and thenintroducing, in place of the chlorine atoms of the resulting product,groups selected from hydroxyl and basic groups, to produce thereby acation-exchange or an anionexchange membrane, respectively.

Thus, sulfochlorinated polyolefine membranes are obtained as anintermediate product. This intermediate product may then be convertedto: (1) cation-exchange membranes, by introducing hydroxyl groups inplace of the chlorine atoms; (2) anion exchange membranes, byintroducing basic groups in place of the chlorine atoms; or (3)membranes having both cation-exchange and anionexchange portions, aswill be described more fully below.

The polyolefines used are either polyethylene or polypropylene havingmolecular weights above 5000.

The sulfochlorination may be effected by reacting the sheet withsulfuryl chloride, in the liquid or vapor state, while irradiated withactinic light. Alternatively, the sulforchlorination may be effected byreacting the sheet with sulfur dioxide and chlorine while irradiatedwith actinic li ht.

After the appropriate period of reaction, the sulfochlorinated materialis removed, for example, from the reaction mixture, washed if necessary,and subsequently converted either into anion-active or cation-activeform by introduction of said appropriate substituents.

If, for example, the sulfochlorinated polyefine membrane is hydrolyzedin alkaline solution, a Water insoluble film membrane is obtained whichexhibits cation-exchange properties. Such material has a capacity ofabout 1-2 meq./g., a low electrical resistance (about 1 ohm per cm. orless for films of about 20 microns) and a high degree of permselectivity(e.g. above 90% for K+ in N/ 10; N/ 20 KCl).

If an anion-exchange membrane is to be produced, the hydrolysis stage isreplaced by one or more steps which introduce free basic functions inplace of the chlorine atoms.

Preferably, the free basic pendant functions are those having a basicdissociation constant of not less than 5 X The introduction of the freebasic functions may be accomplished by esterification or by aminolysisof the sulfuryl chloride with polyvalent amines, such astetraethylenepentamine, N,N dimethylaminoethylendiamine,1,3-diaminopropane, or bis (aminopropyl)-piperazine. The product may bemade more strongly basic by alkylating and quaternizing a non-quaternaryamine derivative, for example, with dibromoethylene, methyl bromide ordimethylsulfate.

The thus prepared membranes exhibit good permselective properties (abouttowards C1 in N/ 10: N/20 KCl), a capacity of about 0.8-2 meq./g., and alow electrical resistance (about 2-5 ohms per cm.

The original properties of the polyolefines are substantially modifiedby the sulfochlorination and by the subsequent treatment. The plasticityis considerably decreased by the sulfochlorination and it is furtherdecreased if subjected to heat treatment. Cross-linking is enhanced byusing polyvalent amines for aminolysis and halo-alkyl compoundscontaining more than one reactive halogen for alkylation and therebyquaternization.

The sulfochlorination reaction may be controlled by varying the reactionconditions. The velocity of reaction may be increased by using suitablecatalysts and by irradiation With visible or ultraviolet light, i.e.actinic light. An increased velocity of reaction can also be obtained byadding a suitable polyolefin swelling agent, such as carbontetrachloride or decaline, to the reaction mixture.

The sulfochlorination can also be carried out by means of sulfur dioxideand chlorine preferably under irradiation with visible or ultravioletlight. This reaction may be effected on the starting material as such(which may also be swollen with suitable solvents) or containingappropriate catalysts.

It is also possible to make use of the intermediate product obtained bysulfochlorination in order to produce membranes having both anion andcation activity in different parts of the same sheet. To achieve thisend, the sulfochloride intermediate membrane is partially immersed in anaminolytic solution of low vapour pressure, say a polyethylenepolyamine(eg. as in Example 5 below), whereby the immersed part is converted intoan anion active membrane. The remaining unreacted part of thesulfochlorinated film is hydrolyzed in an alkaline solution of say NaOHin aqueous dioxane (e.g. as in Example 2 below). In this way it becomespossible to obtain integral sheets comprising anion and cation selectiveportions which can otherwise be obtained only with great difiiculty bycementing together individual anion-selective and cation-selectivemembranes.

Membrane obtained by the aforementioned processes have been used in anelectrodialytic water desalination apparatus of 10x20 cm. membranesurface and operated under a current density of 15 ma./cm. The Coulombefficiency of desalination was about 90%.

In the following the invention will be exemplified without beingrestricted to the examples given:

Example 1 A polyethylene film of 0.003 cm. thickness was immersed in amixture of sulfuryl chloride and carbon tetrachloride (321 by volume) inthe presence of 0.25% (w./ v.) of anhydrous AlCl and kept about 35 C.for 8 hours in daylight. After washing in carbon tetrachloride the filmwas hydrolyzed during 1 hour in 5% (weight/volume) solution of sodiumhydroxide in a water bath. The resultant film had an electricalresistance of 1 ohm/cm. and permselectivity of 92% for K+ ions in a N/lOKCl solution.

Example 2 A polyethylene film of 0.009 cm. thickness was introduced intoa mixture of sulfurylchloride and carbon tetra- 3 chloride (4:1 byvolume) saturated with HCl gas. The reaction was carried out during twohours at a temperature about 35 C. under irradiation with a 75 w.mercury lamp. The film was hydrolyzed for 12 hours in a w./v. solutionof NaOH in 1.1 dioxane-water at room temperature. Its resistance was 3ohms/cm. and its capacity similar to that of the film described in thefirst example.

Example 3 A film of polyethylene of 0.01 cm. thickness was reactedduring two hours with a gaseous mixture of sulfur dioxide and chloride,which was passed through carbon tetrachloride. The reaction was carriedout under irradiation by direct sunlight for two hours. The thusobtained chlorosulfonated product was subjected to hydrolysis asdescribed in Example I. A film having electric resistance of 5 ohm/cm.in N/ NaCl solution was obtained. The capacity of the material was 0.9meq./g. The permselectivity of the membrane was 87% towards K+ ions in aN/ 10 KCl solution.

Example 4 A film of polyethylene of 0.009 cm. thickness was reacted withsulfuryl chloride vapour under irradiation with direct sunlight duringtwo hours. After washing with carbon tetrachloride the film was immersedin a solution of 1 part by volume of ethylenediarnine .in two volumes ofdry dioxane and kept at room temperature for 10 hours. The resultingfilm was quaternized with 50% (vol.) alcoholic ethylene dibromide. Thethus obtained film had an electric resistance of 5 ohms/cm Thepermselectivity for Cl ions in a N/10 KC! solution was about 90%.

Example 5 A film of polyethylene of 0.005 cm. thickness was immersed ina mixture of 1 volume sulfuryl chloride (containing free C1 with 1volume carbon tetrachloride which contained 0.25% AlCl and was saturatedwith HC]. gas. It was irradiated with direct sunlight for 1% hours,washed in carbon tetrachloride and aminolysed in tetraethylenepentamineat 80 C. for 2 hours. The resulting membrane had 3 ohms/cm. resistanceand 85% permselectivity for Clions.

Example 6 A 0.2 mm. thick polypropylene sheet was softened overnight byimmersion in decaline. It was then suspended in a glass walled tank andilluminate-d in a 1:2 mixture of Cl :SO with incandescent lamps for 5hours. After sulfochlorination one part of it was hydrolyzed in 10% NaOHsolution at 60 C. for 4 hours yielding a permselective membrane of 95%permselectivity and 2 ohms per cm. resistance in N/ 10 KC] solution.Another part of the membrane was reacted withN,N-dimethylamino-3-aminopropane at room temperature for two days,alkylated in a 20% solution of methylbromide in alcohol and equilibratedin KCl solution after washing in water. It yielded an anion selectivemembrane of 93% permselectivity and 4 ohms per cm. resistance in N/ 10KCl.

We claim:

1. A process for the production of permselective membranes for use inelectrodialysis, which comprises sulfochlorinating a polyolefine sheetin heterogenous reaction so as to result in a substantiallywater-insoluble product, said polyolefine being selected from the groupconsisting of polyethylene and polypropylene and having a molecularweight above 5000; and introducing, in place of the chlorine atoms of.the resulting product, groups selected from hydroxyl and basic groups,to produce thereby a cationexchange or an anion-exchange membrane,respectively, said basic groups being selected from amines andquaternary ammonium derivatives.

2. A process as defined in claim 1, wherein the sulfochlorination iseffected by reacting the sheet with sulfuryl chloride while irradiatedwith actinic light.

3. A process as defined in claim 1, wherein the sulfochlorination iseffected by reacting the sheet with sulfur dioxide and chlorine whileirradiated with actinic light.

4. A process as defined in claim 1, wherein hydroxyl groups areintroduced in place of the chlorine atoms by hydrolysis in an alkalinesolution, resulting in a cationexchange membrane.

5. A process as defined in claim 1, wherein basic groups are introducedin place of the chlorine atoms by aminolysis with a polyvalent amine,resulting in an anionexchange membrane.

6. A process as defined in claim 1, wherein polyvalent amine groups areintroduced in place of the chlorine atoms and are made more stronglybasic by quaternizing said amine groups, resulting in an anion-exchangemembrane.

7. A process as defined in claim 1, wherein the process is effected inthe presence of a swelling agent for the polyolefine sheet.

8. A process as defined in claim 1, wherein one part of the sheet ismade anion selective by introducing in that one part basic groups inplace of the chlorine atoms, said basic groups being selected fromamines and quaternary ammonium derivatives, and another part of thesheet is made cation selective by introducing in that part hydroxylgroups in place of the chlorine atoms.

9. A process as defined in claim 1, wherein the polyolefine sheet ispolyethylene.

References Cited UNITED STATES PATENTS 2,962,454 11/1960 McRae et al.260-2.2 3,314,925 4/1967 King 260-793 2,933,460 4/1960 Richter et al.260-2.1 2,212,786 8/1940 McQueen 26079.3 2,891,916 6/1959 Hwa 260-222,906,715 9/1959 Hagge et al. 2602.1

FOREIGN PATENTS 747,948 4/1956 Great Britain.

OTHER REFERENCES Fieser and Fieser, Organic Chemistry, Heath 8: Co.,Boston, 1950, pp. 44-45.

Frilette, Journal of Physical Chemistry, vol. 60, 1956, pp. 435-439.

WILLIAM H. SHORT, Primary Examiner.

C. A. WENDEL, M. GOLDSTEIN, Assistant Examiners.

1. A PROCESS FOR THE PRODUCTION OF PERMSELECTIVE MEMBRANES FOR USE INELECTODIALYSIS, WHICH COMPRISES SULFOCHLORINATING A POLYOLEFINE SHEET INHETEROGENOUS REACTION SO AS TO RESULT IN A SUBSTANTIALLY WATER-INSOLUBLEPRODUCT, SAID POLYOLEFINE BEING SELECTED FROM THE GROUP CONSISTING OFPOLYETHYLENE AND POLYPROPYLENE AND HAVING A MOLECULAR WEIGHT ABOVE 5000;AND INTRODUCING, IN PLACE OF THE CHLORINE ATOMS OF THE RESULTINGPRODUCT, GROUPS SELECTED FROM HYDROXYL AND BASIC GROUPS, TO PRODUCETHEREBY A CATIONEXCHANGE OR AN ANION-EXCHANGE MEMBRANE, RESPECTIVELY,SAID BASIC BEING SELECTED FROM AMINES AND QUATERNARY AMMONIUMDERIVATIVES.